Method for manufacturing light emitting device

ABSTRACT

To provide a bright and highly reliable light-emitting device. An anode ( 102 ), an EL layer ( 103 ), a cathode ( 104 ), and an auxiliary electrode ( 105 ) are formed sequentially in lamination on a reflecting electrode ( 101 ). Further, the anode ( 102 ), the cathode ( 104 ), and the auxiliary electrode ( 105 ) are either transparent or semi-transparent with respect to visible radiation. In such a structure, lights generated in the EL layer ( 103 ) are almost all irradiated to the side of the cathode ( 104 ), whereby an effect light emitting area of a pixel is drastically enhanced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting device using a thinfilm that is made of a luminous material. Further, the present inventionrelates to electric equipment using the light-emitting device as adisplay portion or a light source.

2. Description of the Related Art

In recent years, development is proceeding in a light-emitting device(hereinafter referred to as an EL light-emitting device) employing aluminous element (hereinafter referred to as an EL element) that uses athin film (hereinafter referred to as an EL film) made of a luminousmaterial that provides EL (Electro Luminescence). The EL device iscalled a light emitting device or a light emitting diode or OLED(Organic Light Emission Diode). The EL (electroluminescent) devicesreferred to in this specification include triplet-based light emissiondevices and/or singlet-based light emission devices, for example. The ELlight-emitting device has an EL element that is composed of an anode, acathode, and an EL film sandwiched therebetween. The emission of lightcan be attained from the EL light-emitting device by applying a voltagebetween the anode and the cathode. In particular, an organic film thatis used as the EL film is referred to as an organic EL film. Note that aluminous material in which EL can be obtained includes a luminousmaterial that luminesces via a singlet excitation and a luminousmaterial that luminesces via a triplet excitation.

A metal that has a small work function (typically a metal belonging toGroup 1 or Group 2 of the periodic table) is mostly used as the cathode,and a transparent oxide conductive film such as a compound film ofindium oxide and tin oxide (ITO) is mostly used as the anode. Therefore,the emission of light attained is visible after the light is transmittedthrough the anode.

Recently, development is proceeding in an active matrix type ELlight-emitting device in which the control of the emission of light bythe EL elements provided in respective pixels is through the use of aTFT (thin film transistor), and the development thereof has reached astage where trial products have been released. All these trial productsuse a pixel electrode as the anode, and hence the structures thereof aresuch that the light generated by the EL elements is irradiated to theside of the TFT.

However, because light is no transmitted to the regions where the TFTsand wirings are formed in such structures, a light emitting area(hereinafter referred to as an effect light emitting area) that canactually be seen is reduced drastically. Therefore, the necessity ofraising the luminance of the light emitted in order to obtain a brightimage leads to the result of hastening the deterioration of the organicEL film.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve the above problem,and therefore has an object to provide a bright and highly reliablelight-emitting device. Further, another object of the present inventionis to provide highly reliable electric equipment that uses thelight-emitting device as its display portion or light source.

The present invention is characterized in the employment of an ELelement 100 having a structure shown in FIG. 1. In FIG. 1, referencenumeral 101 denotes a reflecting electrode that is made of a metallicfilm. It is preferable that a metallic film that has a high reflectanceis used as the reflecting electrode 101. An aluminum film (aluminumalloy film or an aluminum film containing a dopant) or a silver thinfilm may be used. In addition, the conductive film performed by aluminumplating or silver plating may also be used as the reflecting electrode101.

Next, reference numeral 102 denotes an anode of the EL element 100 whichis made of a transparent conductive film (hereinafter referred to as atransparent conductive film) with respect to visible radiation. It is tobe noted that transparency with respect to the visible radiation (lightof visible radiation region) indicates that the visible radiationtransmits at a transmittance of between 80% and 100%. In case of usingan oxide conductive film (typically a compound film of indium oxide andtin oxide or a compound film of indium oxide and zinc oxide) as thetransparent conductive film, it is preferable that the film thicknessthereof is formed between 10 and 200 nm (preferably between 50 and 100nm).

At this point, a work function of the anode 102 determines a holeinjection barrier, and the reflecting electrode 101 reflects the lightemitted from the EL element and applies a uniform voltage to the anode102 at the same time.

Next, reference numeral 103 denotes an EL layer. The EL layer 103includes an EL film that has a single layer or multiple layers. It is tobe noted that the EL film may be an organic EL film or an inorganic ELfilm, or it may be formed by laminating those films. Further, thestructure of the EL layer 103 may be any known structure. In otherwords, throughout this specification, the EL layer is a layer formed byfreely combining an electron injection layer, an electron transportlayer, and an EL film (also referred as a light-emitting layer). Ofcourse, the EL film may be a low molecular weight or a high molecularweight film.

Reference numeral 104 denotes a cathode of the EL element 100. Ametallic film having a small work function (about −3.5 to −3.8 eV) isused as the cathode 104. A metallic film containing an element thatbelongs to Group 1 or Group 2 of the periodic table may be used as themetallic film having such a work function. Therefore, in the presentinvention, it is desirable that a 10 to 70 nm thick (preferably between20 and 50 nm) metallic film containing an element that belongs to Group1 or Group 2 of the periodic table is used as the cathode 104.

Visible radiation can be transmitted through such a metallic film as theabove, which has a thin film thickness. Thus, the cathode 104 can beused as a transparent electrode to visible radiation.

Next, reference numeral 105 denotes an electrode, which is made of thetransparent conductive film, in contact with the cathode (hereinafterreferred to as an auxiliary electrode). An oxide conductive filmtypified by a compound film of indium oxide and tin oxide or a compoundfilm of indium oxide and zinc oxide may be used as the auxiliaryelectrode 105. The film thickness thereof may be formed to between 10and 200 nm (preferably between 50 and 100 nm). At this point, a workfunction of the cathode 104 determines the hole injection barrier, andthe auxiliary electrode 105 applies a uniform voltage to the cathode104.

When the EL element has the above-described structure, the lightgenerated at the EL layer (strictly the EL film contained in the ELlayer) can be observed from the side of the auxiliary electrode 105 (theupper direction in FIG. 1). This fact can be easily comprehended byconsidering that the light advancing to the side of the anode 102 ismostly reflected by the reflecting electrode 101.

An effect of the present invention is in that the extraction of theemission of light of the EL light-emitting device from the side of thecathode, which in the prior art had been difficult, can now be carriedout with ease. This effect is particularly remarkable during theformation of the active matrix type EL light-emitting device.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a diagram showing a cross sectional structure of an ELelement;

FIGS. 2A and 2B are diagrams showing cross-sectional structures of alight-emitting device;

FIGS. 3A to 3E are diagrams showing a process of manufacturing thelight-emitting device;

FIGS. 4A to 4D are diagrams showing the process of manufacturing thelight-emitting device;

FIGS. 5A and 5B are diagrams showing a top structure and a circuitconfiguration of a pixel of the light-emitting device;

FIG. 6 is a diagram showing a cross-sectional structure of thelight-emitting device;

FIG. 7 is a diagram showing a top structure of the light-emittingdevice;

FIGS. 8A to 8F are diagrams showing specific examples of electronicequipments; and

FIGS. 9A and 9B are diagrams showing specific examples of electronicequipments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment mode of the present invention will be explained withreference to FIGS. 2A and 2B. In FIG. 2A, reference numeral 201 denotesa substrate on which an element is formed (hereinafter referred to as anelement-forming substrate). In the present invention, any material maybe used as the substrate. Glass (including quartz glass), crystallizedglass, single crystal silicon, ceramic, metal, or plastic may be used asthe substrate.

A pixel 202 is formed on the element-forming substrate 201, and thepixel 202 includes a switching TFT 203 and a current control TFT 204.Note that three pixels corresponding to each of the colors red, green,and blue are illustrated in FIG. 2A. The switching TFT 203 functions asa switch for taking a video signal into the pixels, and the currentcontrol TFT 204 functions as a switch for controlling a current flowingto an EL element. At this point, a drain of the switching TFT 203 iselectrically connected to a gate of the current control TFT 204.

There is no limit placed on the structure of the switching TFT 203 andthe current control TFT 204, but the structures thereof may be a topgate type (typically a planar type) or a bottom gate type (typically aninverted stagger type). In addition, an N channel TFT or a P channel TFTmay be used to form both the switching TFT 203 and the current controlTFT 204.

The switching TFT 203 and the current control TFT 204 are covered by aninterlayer insulating film 204, and on the top thereof, a drain of thecurrent control TFT 204 and a pixel electrode 207 a are electricallyconnected via a conductor 206. Further, an anode 207 b made of atransparent conductive film is laminated on the pixel electrode 207 a(corresponding to the reflecting electrode 101 of FIG. 1). It is to benoted that resin that has conductivity by dispersing metallic particlestherein (typically an anisotropic conductive film) may be used as theconductor 206. Of course, the pixel electrode 207 a may be directlyconnected to the drain of the current control TFT 204.

In the embodiment mode, a concave portion that originates in a contacthole will not be formed in the pixel electrode 207 a by employing theconductor 206. Such a concave portion can also be a cause of thedeterioration of the organic EL layer, and hence is not preferred. Thatis, the pixel electrode 207 a is leveled by employing the conductor 206as in the embodiment mode, thereby being capable of suppressing thedeterioration of the organic EL layer and obtaining a uniform emissionof light.

Next, reference numeral 208 denotes an insulating film provided in a gapbetween the adjacent pixel electrode 207 a. The insulating film 208 isformed so as to cover a step that is formed at the edge portion of thepixel electrode 207 a. By keeping the organic EL layer at a distancefrom the edge portion of the pixel electrode 207 a, the insulating film208 has an effect of suppressing the influence of an electric fieldconcentration in the edge portion of the pixel electrode 207 a.

Note that the insulating film 208 is referred to as a bank throughoutthis specification. Resin, a silicon oxide film, a silicon nitride film,or a silicon nitride oxide film can be used as the bank 208. Inparticular, resin has a low relative dielectric constant, and thereforeis effective in suppressing the electric field concentration in the edgeportion of the pixel electrode 207 a.

Reference numeral 209 denotes an organic EL layer luminescing red color,reference numeral 210 denotes an organic EL layer luminescing greencolor, and reference numeral 211 denotes an organic EL layer luminescingblue color. The structure of the organic EL layers 209 to 211 may beknown structures. As in the embodiment mode, in case of forming theorganic EL layers separately for each pixel, the evaporation method ispreferably performed.

A cathode 212, which is provided covering the organic EL layers 209 to211, is an alloy film made of evaporating both the aluminum and lithiumtogether (hereinafter referred to as an Al—Li film). The film thicknessthereof is formed to between 10 and 70 nm (typically between 20 and 50nm). In addition, an auxiliary electrode 213 formed to a thickness ofbetween 10 and 200 nm (preferably between 50 and 100 nm) is providedthereon.

Further, a substrate 214 that is provided in opposition to theelement-forming substrate (hereinafter referred to as an opposingsubstrate) has a spacer 215 made of resin and a passivation film 216which are formed thereon. The opposing substrate 214 is bonded to theelement-forming substrate 201 by a sealing member (not shown in thefigure). The height of the spacer 215 is not particularly limited, butthe height may be between 1 and 3 μm. Also, as the passivation film 216,it is preferable to use an insulating film having a high transmittanceto suppress degas from the spacer 215. For instance, a silicon nitridefilm, a silicon nitride oxide film, a tantalum oxide film, or a carbonfilm (preferably a diamond like carbon film) may be used.

It is further preferable to fill a space 217 that is formed between theelement-forming substrate 210 and the opposing substrate 214 withnitrogen gas or noble gas. It is desirable that an absorbent (substancehaving absorbency) is provided in the space 217 and moisture, oxygen, orgas generated from the resin is preferably absorbed.

The detailed structure of the EL element 218 thus formed is shown inFIG. 2B. The pixel electrode 207 a also serves as the reflectingelectrode, and therefore the structure of the EL element 218 is similarto the structure of the EL element of the present invention shown inFIG. 1.

By adopting the structure shown in the embodiment mode of the presentinvention, the emission of light generated by the EL element 218 isirradiated towards the direction indicated by the arrow (a directionindicating the irradiation direction of light). Therefore, even if thearea of the TFT and the wiring included in the pixel is large, theeffect light emitting area is prescribed by the area of the pixelelectrode 207 a, making it possible to secure a sufficiently large area.In other words, a satisfactorily bright image can be attained withoutraising the luminance of the emitted light.

This means that the driving voltage of the EL element is set at a lowlevel to reduce the consumption power of the EL light-emitting device.Further, this means that the driving voltage of the EL element issimilarly set at a low level to suppress the deterioration of theorganic EL layer, thereby raising the reliability of the ELlight-emitting device.

Embodiment 1

Embodiment 1 will be explained with reference to FIGS. 3A to 5B. Notethat shown in FIGS. 3A to 4D are cross sectional views of manufacturingprocesses in a pixel portion. Furthermore, the top view of a pixelformed in accordance with Embodiment 1 (a top view at the point of theformation of an anode) is shown in FIG. 5A, and a final circuitconfiguration of the pixel is shown in FIG. 5B. It is to be noted thatthe reference numerals used in FIGS. 5A and 5B correspond to those usedin FIGS. 3A to 4D.

First, as shown in FIG. 3A, a glass substrate 301 is prepared as theelement-forming substrate, and an insulating film 302 made of a siliconoxide film is formed thereon to a thickness of 200 nm. The insulatingfilm 302 may be formed by employing low pressure thermal CVD, plasmaCVD, sputtering, or evaporation.

A crystalline silicon film 303 is next formed to a thickness of 50 nm onthe insulating film 302. A known method may be used as the formationmethod of the crystalline silicon film 303. An amorphous silicon filmmay be crystallized into the crystalline silicon film 103 by using asolid laser or an excimer laser, or the amorphous silicon film may becrystallized by performing heat treatment (furnace annealing). InEmbodiment 1, the amorphous silicon film is crystallized by irradiatingby means of excimer laser using XeCl gas.

Next, as shown in FIG. 3B, the crystalline silicon film 303 is patternedto thereby form island-like crystalline silicon films 304 and 305(hereinafter referred to as active layers). Then a gate insulating film306 made of a silicon oxide film is formed to a thickness of 80 nm so asto cover the active layers. Gate electrodes 307 and 308 are furtherformed on the gate insulating film 306. As a material of the gateelectrodes 307 and 308 in Embodiment 1, a 350 nm thick tungsten film ora tungsten alloy film is used. Of course, other known materials can beused as the material of the gate electrode.

Note that in Embodiment 1, a connecting wiring 309 is formedsimultaneously at this point. The connecting wiring 309 is a wiring forelectrically connecting a source of the current control TFT and acurrent supply line later.

As shown in FIG. 3C next, using the gate electrodes 307 and 308 asmasks, an element (typically boron) that belongs to Group 13 of theperiodic table is doped. A known doping method may be used. Thus,impurity regions (hereinafter referred to as p-type impurity regions)310 to 314 which indicate p-type conductivity are formed. Further,channel forming regions 315 a, 315 b, and 316 are demarcated right underthe gate electrodes. Note that the p-type impurity regions 310 to 314become a source region or a drain region of a TFT.

The doped element that belongs to Group 13 of the periodic table, whichis doped, is activated by performing heat treatment. This activationprocess is performed by furnace annealing, laser annealing, or lampannealing, or may be performed by a combination thereof. In Embodiment1, the heat treatment is conducted under a nitrogen atmosphere at atemperature of 500° C. for 4 hours.

However, it is preferable to set the oxygen concentration in thetreatment atmosphere of the activation process to 1 ppm or less(preferably 0.1 ppm or less). If the oxygen concentration is high, thesurfaces of the gate electrodes 307 and 308 and the surface of theconnecting wiring 309 will be oxidized. As a result, it will becomedifficult to obtain an electrical connection to a gate wiring and acurrent supply line, which will be formed in a later process.

Note that it is effective to perform a hydrogenation treatment aftercompleting the activation process. The known hydrogen annealingtechnique or the plasma hydrogenation technique may be used in thehydrogenation treatment.

As shown in FIG. 3D, a current supply line 317 is formed so as tocontact the connecting wiring 309. By forming such a structure (the topview thereof is indicated by a region denoted by reference numeral 501in FIG. 5A), the connecting wiring 309 and the current supply line 317are electrically connected to each other. Note that although not shownin the figure, a gate wiring (wiring denoted by reference numeral 502 inFIG. 5A) is formed simultaneously at this point to thereby beelectrically connected to a gate electrode 307. The top view thereof isindicated by a region denoted by reference numeral 503 in FIG. 5A.

In the region denoted by reference numeral 503, a design is maderedundant such that a gate wiring 502 has a convex portion in order tosecure a part that does not override the gate electrode 307. By adoptingsuch a structure, even if the gate wiring 502 is cut at the part whereit overrides the gate electrode 307, electrically cutting the gatewiring 502 at that point can be prevented. In addition, the structuresuch that the gate electrode 307 is processed into a U-shape is aredundant design for the purpose of applying a voltage to both the gateelectrodes without fail.

The current supply line 317 and the gate wiring 502 are made of ametallic film that has a lower resistance than that of the metallic filmforming the connecting wiring 309 and the gate electrode 307. A metallicfilm containing aluminum, copper, or silver is preferably used. That is,a metallic film having a high workability is used for forming a gateelectrode that demands fine patterning accuracy, and a metallic filmhaving a low resistance is used for forming a bus line (gate wiring andcurrent supply line in Embodiment 1) that demands a low resistivity.

Upon formation of the gate wiring 502 and the current supply line 309, afirst interlayer insulating film 318 made of a silicon oxide film isformed to a thickness of 800 nm. Plasma CVD may be employed as theformation method thereof. Other inorganic insulating films may be usedas the first interlayer insulating film 318, or resin (organicinsulating film) may be used.

As shown in FIG. 3E next, a contact hole is formed in the firstinterlayer insulating film 318 to thereby form wirings 319 to 322. InEmbodiment 1, a metallic wiring made of a three-layered structure oftitanium, aluminum, and titanium is used as the wirings 319 to 322. Ofcourse, any material may be used as long as it is a conductive film. Thewirings 319 to 322 become source wirings or drain wirings of the TFT.

The drain wiring 322 of the current control TFT is electricallyconnected to the connecting wiring 309. As a result, the drain of acurrent control TFT 402 is electrically connected to the current supplyline 317.

A switching TFT 401 and the current control TFT (EL driving TFT) 402 arethus completed in this state. Both the TFTs are formed of a P channelTFT in Embodiment 1. However, the switching TFT 401 is formed such thatthe gate electrodes cut across the active layers in two places,resulting in forming a structure in which two channel forming regionsare connected in series. By forming such a structure, an OFF currentvalue (a current that flows when the TFT is turned OFF) can beeffectively suppressed.

As shown in FIG. 5A, a storage capacitor 504 is further formed in thepixel. The storage capacitor 504 is composed of a semiconductor layer505 that is electrically connected to the drain of the current controlTFT 402, the gate insulating film 306, and a capacitor wiring 506. Thecapacitor wiring 506 is formed at the same time as the gate wiring 502and the current supply line 317, and also serves as a wiring forelectrically connecting the gate electrode 308 and a connecting wiring507. It is to be noted that the connecting wiring 507 is electricallyconnected to the drain wiring (in some cases, functioning as a sourcewiring) 320 of the switching TFT 401.

Upon formation of the wirings 319 to 322, a passivation film 323 made ofa silicon nitride film or a silicon nitride oxide film is formed to athickness of 200 nm. A hydrogenation treatment either before or afterforming the passivation film 323 is performed, thereby being capable ofimproving the electric characteristic of the TFTs.

As shown in FIG. 4A, a second interlayer insulating film 324 made ofacrylic is formed to a thickness of 1 μm. After opening a contact hole325, an anisotropic conductive film 326 is formed. In Embodiment 1,acrylic having silver particles dispersed therein is used as theanisotropic conductive film 326. In addition, it is preferable to formthe anisotropic conductive film 326 to about a thickness that is thickenough to level the contact hole 325. The anisotropic conductive film326 is formed to a thickness of 1.5 μm by spin coating in Embodiment 1.

Next, the anisotropic conductive film 326 is etched by plasma employingoxygen gas. This process is continued until the second interlayerinsulating film 324 is exposed. When the etching process is completed, aconductor 327 is formed to have a shape shown in FIG. 4B.

Upon formation of the conductor 327, an aluminum film doped withscandium or titanium and an ITO film (compound film of indium oxide andtin oxide) are laminated thereon. Then the films are etched, together toform a pixel electrode 328 and an anode 329. In Embodiment 1, thealuminum film is formed to have a thickness of 200 nm, and the ITO filmis formed to a thickness of 100 nm. Further, the ITO film may be etchedwith ITO-04N (product name of an ITO film etching solution manufacturedby Kanto Chemistry Inc.), and the aluminum film may be etched by a dryetching method employing a mixed gas of carbon tetrachloride (SiCl₄) andchlorine (Cl₂).

The cross-sectional structure of FIG. 4B thus obtained corresponds tothe cross-sectional structure taken along the line A-A′ in FIG. 5A.

As shown in FIG. 4C, a bank 330 made of an insulating film is formednext. In Embodiment 1, acrylic is used to form the bank 330. Uponformation of the bank 330, ultraviolet light is irradiated to the anode329 under an oxygen atmosphere to thereby perform surface treatmentthereof. This process has an effect of increasing the work function ofthe anode 329, and has a further effect of removing the contaminationson the surface of the anode 329.

Then organic EL layers 331 and 332 are each formed to have a thicknessof 50 nm. Note that the organic EL layer 331 is an organic EL layerluminescing blue color and that the organic EL layer 332 is an organicEL layer luminescing red color. Note that although not shown in thefigure, an organic EL layer luminescing green color is formed at thesame time. In Embodiment 1, the organic EL layers for each pixel areformed separately by the evaporation method that employs a shadow mask.Of course, the organic EL layers may be formed separately by using theprinting method and the ink jet method.

The organic EL layers 331 and 332 are formed to have a laminationstructure in Embodiment 1. To be more specific, CuPc (CopperPhthalocyanine) is used as a hole injection layer. In this case, acopper phthalocyanine film is first formed on all the pixels.Thereafter, a light-emitting layer luminescing red color, alight-emitting layer luminescing green color, and a light-emitting layerluminescing blue color, respectively, are formed thereon to each of thepixels corresponding to the colors red, green, and blue.

It is to be noted that when forming the light-emitting layer luminescinggreen color, Alq₃ (tris-8-quinolilite-aluminum complex) is used as thecore material of the light-emitting layer, and quinacridon or coumarin 6is doped as the dopant. Further, when forming the light-emitting layerluminescing red color, and CDJT, DCM1, or DCM2 is doped as the dopant.When forming the light-emitting layer luminescing blue color, BAlq₃ (a 5ligand complex having 2-methyl-8-quinolinol and a mixed ligand of aphenol conductor) is used as the core material of the light-emittinglayer, and perylene is doped as the dopant.

Of course, the present invention is not necessarily limited to the aboveorganic materials, and known low molecular weight organic EL materials,high molecular weight organic EL materials, and inorganic EL materialsmay be used. In case of using a high molecular weight organic ELmaterial, an application method can also be employed.

Upon forming the organic EL layers 331 and 332 in accordance with theabove steps, an MgAg film (metallic film in which 1% to 10% of silver(Ag) is doped into magnesium (Mg)) is formed to have a thickness of 20nm as a cathode 333. An ITO film is further formed to have a thicknessof 150 nm as an auxiliary electrode 334. An EL element 400 that iscomposed of the anode 329, the organic EL layer 332, and the cathode 333is thus formed. In Embodiment 1, the EL element 400 functions as aluminous element.

Next, as shown in FIG. 4D, a spacer 336 made of resin and an opposingside passivation film 337 made of a tantalum oxide film or a diamondlike carbon film are formed on an opposing substrate 335. Then, theelement-forming substrate 301 and the opposing substrate 335 are bondedtogether by using a sealing member not shown in the figure. The opposingside passivation film 337 has an effect of preventing degas from thespacer 336 made of resin. Note that in Embodiment 1, the substrate thatincludes the elements formed thereon is referred to as theelement-forming substrate. Furthermore, the substrate that includes thespacer and the opposing side passivation film formed thereon is referredto as the opposing substrate.

It is to be noted that the bonding process of both the substrates isperformed under an argon atmosphere. As a result, a space 338 is filledwith argon. Of course, inert gas such as nitrogen gas or noble gas maybe used as the gas to be filled in the space 338. In addition, it ispreferable to provide a material that absorbs oxygen or moisture in thespace 338. Further, instead of leaving the space 338 empty as a space,resin may be filled therein.

The switching TFT (P channel TFT in Embodiment 1) 401 and the currentcontrol TFT (P channel TFT in Embodiment 1) 402 are thus formed in thepixel in accordance with the manufacturing processes shown above. InEmbodiment 1, because all the TFTs are formed of the P channel TFT, themanufacturing processes are extremely simple and easy. Of course, an Nchannel TFT may be used as the switching TFT and/or the current controlTFT. A known technique may be employed to manufacture the N channel TFTand the structure thereof is not particularly limited.

The leveling of steps is performed by the second interlayer insulatingfilm 324. Further, because the drain wiring 321 of the current controlTFT 402 and the pixel electrode 328 are electrically connected to eachother by using the conductor 327 filling the contact hole 325, the pixelelectrode 328 has a high flatness. Therefore, the emission of light fromthe pixels can be made uniform since the uniformity of the filmthickness of the organic EL layer 332 can be enhanced.

The principal characteristic of the present invention is in that lightemitted from the EL element 400 is irradiated in the direction towardthe side of the opposing substrate 335. Thus, almost the entire area ofthe pixels become the effect light emitting area, and the area of thepixel electrode 328 substantially determines the effect light emittingarea. Therefore, it becomes possible to realize a high aperture ratio of80 to 95%.

Embodiment 2

In Embodiment 2, an explanation will be made with reference to FIG. 6 onan EL light-emitting device having a pixel with a structure that isdifferent from that of the EL light-emitting device shown in FIG. 2.Note that in Embodiment 2, the structure of the EL light-emitting devicemay be manufactured by adding a few changes to the structure of FIG. 2,and hence explanations will be made on the points that are differentfrom those of FIG. 2. Therefore, the embodiment mode may be referencedconcerning the explanation of the parts that are denoted by the samereference numerals with those of FIG. 2.

In Embodiment 2, upon forming a contact hole in the interlayerinsulating film 205, a pixel electrode 601 a and anode 601 b are formedin this state. Then, an insulating film 602 is formed to fill up theconcave portion formed by the contact hole. The insulating film 602 iscalled a filling-up insulating film in Embodiment 2. The filling-upinsulating film 602 can be formed at the same time with the bank 208 sothat any particular process does not have to be added to themanufacturing processes.

Similar to the conductor 206 of FIG. 2, the filling-up insulating film602 is a film for suppressing the deterioration of the organic EL layerwhich originates at the concave portion caused by the contact hole. Atthis point, it is preferable to set the height between the top of thefilling-up insulating film 602 and the anode 601 b to between 100 and300 nm. If the height exceeds 300 nm, a step is formed and there arecases where this step becomes a cause of promoting the deterioration ofthe organic EL layer. Further, if the height is less than 100 nm, thereis a concern that the effect of the bank 208 (the effect of suppressingthe influence of the electric field concentration in the edge portion ofthe pixel electrode), which is formed at the same time, is reduced.

After the formation of the anode 601 a, an acrylic film is formed tohave a thickness of 500 nm by spin coating in Embodiment 2. Then, oxygengas is formed into plasma to thereby perform etching to the acrylic filmuntil the film thickness thereof (only the film thickness outside thecontact hole) reaches 200 nm. Thus, after making the film thickness ofthe acrylic film thin, patterning is performed to form the bank 208 andthe filling-up insulating film 602.

A top structure of the pixel in Embodiment 2 is shown here in FIG. 7.The cross-sectional view taken along the line A-A′ of FIG. 7 correspondsto FIG. 6. Note that the opposing substrate 214 and the spacer 215 arenot shown in FIG. 7. In addition, the basic structure of the pixel isthe same as that of FIG. 5, and therefore the detail explanation thereofis omitted.

In FIG. 7, the bank 208 is formed so as to hide the step at the edgeportion of the pixel electrode 601 a and the anode 601 b. The filling-upinsulating film 602 is formed such that a portion of the bank 208 isprotruding. Thus, a structure may be such that the protruding insulatingfilm fills up the concave portion formed by the contact hole of thepixel electrode 601 a.

Note that the EL light-emitting device of Embodiment 2 can be readilymanufactured by combining the above-mentioned formation method of thefilling-up insulating film to the manufacturing method of Embodiment 1.

Embodiment 3

Although only the structure of the pixel portion is shown in the ELlight-emitting device illustrated in Embodiment 1, a driver circuit fordriving the pixel portion may be formed integrally therewith on the samesubstrate. When forming the driver circuit, the driver circuit may beformed of an nMOS circuit, a pMOS circuit, or a CMOS circuit. Of course,only the pixel portion may be formed of a TFT, and a driver circuitcontaining an IC chip may be used as an external-attached drivercircuit.

Further, the manufacturing processes in Embodiment 1 are reduced byforming the pixel portion with the P channel TFT only. However, in caseof Embodiment 2, the driver circuit is formed of the pMOS circuit, and adriver circuit containing an IC chip can be used as the driver circuitthat cannot be formed of the pMOS circuit.

Note that the constitution of Embodiment 2 may be implemented by freelycombining it with the constitution of Embodiment 1 or 2.

Embodiment 4

In Embodiment 4, an explanation will be made on an example where anamorphous silicon film is used as an active layer of a switching TFT anda current control TFT that are to be formed in the pixel portion. Aninverted stagger type TFT is known as the TFT using an amorphous siliconfilm. Such a TFT is used in Embodiment 4.

The manufacturing process of the TFT using an amorphous silicon film issimple and easy, on the other hand, it has a drawback in that the sizeof an element is made large. However, in the EL light-emitting device ofthe present invention, the size of the TFT has no influence on theeffect light emitting area of the pixel. Therefore, a more inexpensiveEL light-emitting device can be manufactured by using an amorphoussilicon film as the active layer of the TFT.

Note that the constitution of Embodiment 4 may be implemented by freelycombining it with any of the constitutions of Embodiments 1 to 3.However, in case of combining the constitution of Embodiment 4 with thatof Embodiment 3, it is preferable to externally attach the diver circuitcontaining an IC chip because it is difficult that a driver circuithaving a rapid operational speed is manufactured with the TFT using theamorphous silicon film.

Embodiment 5

In Embodiments 1 through 4, explanations were made in regards to theactive matrix type EL light-emitting device. However, the presentinvention may also be implemented to an EL element of a passive matrixtype EL light-emitting device.

The passive matrix type EL light-emitting device is formed containing astructure where anodes and cathodes are provided in stripe-shape suchthat they are orthogonal to each other and organic EL layers aresandwiched therebetween. The structure shown in FIG. 1 may be employedwhen manufacturing the passive matrix type EL light-emitting device.

Note that the constitution of Embodiment 5 may be implemented by freelycombining it with any of the constitutions of Embodiments 1 to 3.However, in case of combining the constitution of Embodiment 5 with thatof Embodiment 3, the driver circuit containing an IC chip is externallyattached.

Embodiment 6

An example of employing the EL light-emitting device of the presentinvention as a light source of a backlight that is used in a liquidcrystal display or fluorescent display lamp will be explained inEmbodiment 6. In this case, there is no need to separate the EL elementsaccording to the respective pixels. The EL elements implemented by thepresent invention may be used as the luminous elements emitting light ina spread manner.

Further, in the surface of the substrate, the area thereof may be splitinto a plurality of areas such that the light emission of differentcolors can be obtained from the respective areas. The manufacturingprocess of the organic EL layer of Embodiment 1 may be referencedregarding the separate formation of the EL elements.

It is to be noted that the EL element of Embodiment 6 basicallycorresponds to the case where a pixel in Embodiment 1 has been formed tobecome large. Therefore, it is desirable that the contrivance ofcovering the edge portion of the anode with the insulating film isperformed with reference to Embodiment 1.

Embodiment 7

The light-emitting device formed by implementing the present inventioncan be used as a display portion of various kinds of electricequipments. For instance, when appreciating a television broadcast orthe like, a display incorporating a 20 to 40 inch diagonallight-emitting device of the present invention in a casing may be used.Note that a personal computer display, a television broadcast receivingdisplay, and a display for exhibiting all information such as a displayfor displaying announcements are included in the displays having thelight-emitting device incorporated in a casing.

The following can be given as other electronic equipments of the presentinvention: a video camera, a digital camera; a goggle type display (headmounted display); a navigation system; an audio playback device (such asa car audio stereo or an audio component stereo); a notebook typepersonal computer; a game apparatus; a portable information terminal(such as a mobile computer, a portable telephone, a portable gamemachine, or an electronic book); and an image playback device equippedwith a recording medium (specifically, device provided with a displayportion which plays back images in a recording medium and displays theimages). Specific examples of these electronic equipments are shown inFIGS. 8A to 9B.

FIG. 8A shows a display having a light-emitting device incorporated in acasing, and the display contains a casing 2001, a support stand 2002, adisplay portion 2003 and the like. The light-emitting device of thepresent invention can be used as the display portion 2003. Such adisplay is a self-emitting type so that a back light is not necessary.Thus, the display portion can be made thinner than that of a liquidcrystal display.

FIG. 8B shows a video camera, and contains a main body 2101, a displayportion 2102, a sound input portion 2103, operation switches 2104, abattery 2105, an image receiving portion 2106 and the like. Thelight-emitting device of the present invention can be used as thedisplay portion 2102.

FIG. 8C is a portion (right side) of a head mounted EL display, andcontains a main body 2201, a signal cable 2202, a head fixing band 2203,a display portion 2204, an optical system 2205, a light-emitting device2206 and the like. The present invention can be applied to theself-emitting device 2206.

FIG. 8D is an image playback device equipped with a recording medium(specifically, a DVD playback device), and contains a main body 2301, arecording medium (such as a DVD) 2302, operation switches 2303, adisplay portion (a) 2304, a display portion (b) 2305 and the like. Thedisplay portion (a) 2304 is mainly used for displaying imageinformation. The display portion (b) 2305 is mainly used for displayingcharacter information. The light-emitting device of the presentinvention can be used as the display portion (a) 2304 and as the displayportion (b) 2305. Note that the image playback device equipped with therecording medium includes devices such as household game machines.

FIG. 8E shows a mobile computer, and contains a main body 2401, a cameraportion 2402, an image receiving portion 2403, operation switches 2404,a display portion 2405 and the like. The light-emitting device of thepresent invention can be used as the display portion 2405.

FIG. 8F is a personal computer, and contains a main body 2051, a casing2502, a display portion 2503, a keyboard 2504 and the like. Thelight-emitting device of the present invention can be used as thedisplay portion 2503.

Note that if the luminance increases in the future, then it will becomepossible to use the light-emitting device of the present invention in afront type or a rear type projector by expanding and projecting lightcontaining output image information with a lens, an optical fiber or thelike.

In addition, since the light-emitting device conserves power in thelight emitting portion, it is preferable to display information so as tomake the light emitting portion as small as possible. Consequently, whenusing the light-emitting device in a display portion mainly forcharacter information, such as in a portable information terminal, inparticular a portable telephone or an audio playback device, it ispreferable to drive the light-emitting device so as to form characterinformation by the light emitting portions while non-light emittingportions are set as background.

FIG. 9A shows a portable telephone, and contains a main body 2601, asound output portion 2602, a sound input portion 2603, a display portion2604, operation switches 2605, and an antenna 2606. The light-emittingdevice of the present invention can be used as the display portion 2604.Note that by displaying white color characters in a black colorbackground, the display portion 2604 can suppress the power consumptionof the portable telephone.

FIG. 9B shows an audio playback device, specifically a car audio stereo,and contains a main body 2701, a display portion 2702, and operationswitches 2703 and 2704. The light-emitting device of the presentinvention can be used as the display portion 2702. Further, a car audiostereo is shown in Embodiment 7, but a portable type or a householdaudio playback device may also be used. Note that by displaying whitecolor characters in a black color background, the display portion 2704can suppress the power consumption. This is especially effective in aportable type audio playback device.

It is also possible to use the light-emitting device of the presentinvention a sa light source for a back light of a liquid crystal displaydevice (liquid crystal module). The liquid crystal display device,similar to the light-emitting device of the present invention, may beused as a display portion in all the above-mentioned electricequipments. The light-emitting device of the present invention can beprovided in the electric equipments with the liquid crystal displaydevice.

Thus, the application range of the present invention is extremely wide,whereby it may be employed in electric equipments of all fields.Further, the electric equipments of Embodiment 7 may employ thelight-emitting device having any of the constitutions of Embodiments 1through 6.

In the present invention, in the EL element composed of the anode,cathode, and the EL layer sandwiched therebetween, the cathode is madetransparent to visible radiation and the reflecting electrode isprovided under the EL element to thereby make it possible to extractlight from the side of the cathode. As a result, the effect lightemitting area of the pixel is improved sharply, whereby a brightemission of light can be obtained without raising the driving voltage ofthe EL elements.

Further, because the driving voltage can be reduced, suppression of thedeterioration of the EL layer and reduction of the consumption power ofthe light-emitting device can be realized. In other words, it ispossible to provide a bright and highly reliable light-emitting device.In addition, the reliability of the electric equipments using thelight-emitting device of the present invention as the display portion orthe light source can be improved.

1. A method for manufacturing a display device comprising: forming afirst inverted stagger type thin film transistor comprising a firstactive layer comprising amorphous silicon and a second inverted staggertype thin film transistor comprising a second active layer comprisingamorphous silicon over a first substrate; forming a first pixelelectrode over the first inverted stagger type thin film transistor anda second pixel electrode over the second inverted stagger type thin filmtransistor; forming a bank covering an edge portion of the first pixelelectrode and an edge portion of the second pixel electrode; forming afirst light-emitting layer of a first EL element by an evaporationmethod using a first shadow mask over the first pixel electrode and thebank, wherein the first light-emitting layer emits a first color light;forming a second light-emitting layer of a second EL element by anevaporation method using a second shadow mask over the second pixelelectrode and the bank, wherein the second light-emitting layer emits asecond color light; forming a spacer over a second substrate; andpasting the first substrate and the second substrate after forming thespacer so that the spacer is opposed to the bank, wherein the firstcolor is different from the second color.
 2. The method formanufacturing the display device according to claim 1, wherein at leastone of the first and second inverted stagger type thin film transistorsis a current control thin film transistor.
 3. The method formanufacturing the display device according to claim 1, wherein at leastone of the first and second inverted stagger type thin film transistorsis a switching thin film transistor.
 4. The method for manufacturing thedisplay device according to claim 1, wherein at least one of the firstlight-emitting layer and the second light-emitting layer comprises anorganic EL film.
 5. The method for manufacturing the display deviceaccording to claim 1, wherein at least one of the first light-emittinglayer and the second light-emitting layer comprises an inorganic ELfilm.
 6. The method for manufacturing the display device according toclaim 1, wherein a passivation film is located between the spacer andthe bank.
 7. The method for manufacturing the display device accordingto claim 1, wherein pasting the first substrate and the second substratecomprises doing so using a sealing member.
 8. A method for manufacturinga display device comprising: forming a first inverted stagger typeamorphous silicon thin film transistor and a second inverted staggertype amorphous silicon thin film transistor over a first substrate;forming a first pixel electrode over the first inverted stagger typeamorphous silicon thin film transistor and a second pixel electrode overthe second inverted stagger type amorphous silicon thin film transistor;forming a bank covering an edge portion of the first pixel electrode andan edge portion of the second pixel electrode; forming a firstlight-emitting layer of a first EL element by an evaporation methodusing a first shadow mask over the first pixel electrode and the bank,wherein the first light-emitting layer emits a first color light;forming a second light-emitting layer of a second EL element by anevaporation method using a second shadow mask over the second pixelelectrode and the bank, wherein the second light-emitting layer emits asecond color light; forming a spacer over a second substrate; andpasting the first substrate and the second substrate after forming thespacer so that the spacer is opposed to the bank, wherein the firstcolor is different from the second color.
 9. The method formanufacturing the display device according to claim 8, wherein at leastone of the first and second inverted stagger type amorphous silicon thinfilm transistors is a current control thin film transistor.
 10. Themethod for manufacturing the display device according to claim 8,wherein at least one of the first and second inverted stagger typeamorphous silicon thin film transistors is a switching thin filmtransistor.
 11. The method for manufacturing the display deviceaccording to claim 8, wherein at least one of the first light-emittinglayer and the second light-emitting layer comprises an organic EL film.12. The method for manufacturing the display device according to claim8, wherein at least one of the first light-emitting layer and the secondlight-emitting layer comprises an inorganic EL film.
 13. The method formanufacturing the display device according to claim 8, wherein apassivation film is located between the spacer and the bank.
 14. Themethod for manufacturing the display device according to claim 8,wherein pasting the first substrate and the second substrate comprisesdoing so using a sealing member.
 15. A method for manufacturing adisplay device comprising: forming a first inverted stagger type thinfilm transistor comprising a first active layer comprising amorphoussilicon and a second inverted stagger type thin film transistorcomprising a second active layer comprising amorphous silicon over afirst substrate; forming a first pixel electrode over the first invertedstagger type thin film transistor and a second pixel electrode over thesecond inverted stagger type thin film transistor; forming a bankcovering an edge portion of the first pixel electrode and an edgeportion of the second pixel electrode; forming a first light-emittinglayer of a first EL element by an ink jet method over the first pixelelectrode and the bank, wherein the first light-emitting layer emits afirst color light; forming a second light-emitting layer of a second ELelement by an ink jet method over the second pixel electrode and thebank, wherein the second light-emitting layer emits a second colorlight; forming a spacer over a second substrate; and pasting the firstsubstrate and the second substrate after forming the spacer so that thespacer is opposed to the bank, wherein the first color is different fromthe second color.
 16. The method for manufacturing the display deviceaccording to claim 15, wherein at least one of the first and secondinverted stagger type thin film transistors is a current control thinfilm transistor.
 17. The method for manufacturing the display deviceaccording to claim 15, wherein at least one of the first and secondinverted stagger type thin film transistors is a switching thin filmtransistor.
 18. The method for manufacturing the display deviceaccording to claim 15, wherein at least one of the first light-emittinglayer and the second light-emitting layer comprises an organic EL film.19. The method for manufacturing the display device according to claim15, wherein at least one of the first light-emitting layer and thesecond light-emitting layer comprises an inorganic EL film.
 20. Themethod for manufacturing the display device according to claim 15,wherein a passivation film is located between the spacer and the bank.21. The method for manufacturing the display device according to claim15, wherein pasting the first substrate and the second substratecomprises doing so using a sealing member.
 22. A method formanufacturing a display device comprising: forming a first invertedstagger type amorphous silicon thin film transistor and a secondinverted stagger type amorphous silicon thin film transistor over afirst substrate; forming a first pixel electrode over the first invertedstagger type amorphous silicon thin film transistor and a second pixelelectrode over the second inverted stagger type amorphous silicon thinfilm transistor; forming a bank covering an edge portion of the firstpixel electrode and an edge portion of the second pixel electrode;forming a first light-emitting layer of a first EL element by an ink jetmethod over the first pixel electrode and the bank, wherein the firstlight-emitting layer emits a first color light; forming a secondlight-emitting layer of a second EL element by an ink jet method overthe second pixel electrode and the bank, wherein the secondlight-emitting layer emits a second color light; forming a spacer over asecond substrate; and pasting the first substrate and the secondsubstrate after forming the spacer so that the spacer is opposed to thebank, wherein the first color is different from the second color. 23.The method for manufacturing the display device according to claim 22,wherein at least one of the first and second inverted stagger typeamorphous silicon thin film transistors is a current control thin filmtransistor.
 24. The method for manufacturing the display deviceaccording to claim 22, wherein at least one of the first and secondinverted stagger type amorphous silicon thin film transistors is aswitching thin film transistor.
 25. The method for manufacturing thedisplay device according to claim 22, wherein at least one of the firstlight-emitting layer and the second light-emitting layer comprises anorganic EL film.
 26. The method for manufacturing the display deviceaccording to claim 22, wherein at least one of the first light-emittinglayer and the second light-emitting layer comprises an inorganic ELfilm.
 27. The method for manufacturing the display device according toclaim 22, wherein a passivation film is located between the spacer andthe bank.
 28. The method for manufacturing the display device accordingto claim 22, wherein pasting the first substrate and the secondsubstrate comprises doing so using a sealing member.